The invention relates to a flow control valve having a shut-off body constructed as a piston arranged so as to be displaceable inside a cage. The cage comprises several hollow cylindrical cage pipes which are nested in one another in a liquid-tight manner and in a concentric arrangement. These cage pipes have bores therein which are connected to bores in adjacent cage pipes.
In the case of control valves, if only a single resistance were to be arranged in the flow path, the pressure to be reduced from the input pressure p.sub.1 by the pressure difference .DELTA. p to the output pressure p.sub.2 would in the meantime sink by a considerably greater amount than .DELTA. p and would thus accordingly drop below the desired output pressure p.sub.2. Apart from the fact that in the region of the least pressure the medium is subjected to a very high acceleration and thus assumes such high speeds that erosions are promoted. Under such operating conditions there is also the danger that the region of the least pressure passes into the vapor pressure zone or comes too close to this zone, whereby cavitation occurs.
Therefore, in know control valves, the labyrinth principle is used to reduce the pressure of a flowing medium. According to the labyrinth principle several resistances are arranged in series in the flow path, so that each resistance brings about an acceleration of the flowing medium and a corresponding pressure drop in smaller stages. The partial raising again of the pressure in the flow direction behind the resistances is effected in correspondingly small stages. Erosion and cavitation may be avoided by means of such a pressure reduction carried out in stages if, depending on the magnitude of .DELTA.p, an adequate number of resistances is arranged in series.
However, the labyrinth system can be used only to a limited extent in the case of high pressure control valves, since a large number of resistances connected in series leads to a correspondingly large valve structure. Large valves entail large production expenditures, and make their maintenance more expensive, all the more so since corresponding cross-sectional constrictions of the resistances in the individual flow channels enhance the risk of clogging.
Known control valves for high pressures have a displaceably constructed shut-off body mounted in a housing having an inlet, an outlet, and a valve chamber arranged therebetween. A cage having a hollow cylindrical shape is located in the valve chamber. The displaceable shut-off body extends to a larger or smaller extent into the interior of the cage. It has been proposed heretofore to compose the cage for such a control valve of numerous hollow cylindrical cage pipes or sleeves, please see German Patent Publication (DE-OS) No. 2,439,583. In said prior art valve the cage pipes have correspondingly different diameters and are nested in one another in a liquid-tight manner and in a concentric arrangement. Numerous openings are formed in each cage unit. The openings communicate with corresponding openings in an adjacent cage unit.
The flow medium passes in the case of the known valve successively through the cage sleeves so that its pressure is successively reduced in many stages and a high pressure difference or pressure drop, for example, between the pressure of the medium in the interior of the cage and the pressure of the medium outside of the cage may be achieved. Since this pressure drop is achieved successively in stages, a pressure reduction region having a locally large pressure drop can be avoided whereby the danger of cavitation is substantially precluded, so that also no erosion occurs.
However, a disadvantage of the prior art valve consists in that, for a high pressure difference, a large number of cage sleeves nested one in the other is needed, whereby the known valve becomes correspondingly involved and expensive.